Electrical control system



om"n 15', 1946.

O. E. BOWLUS ELECTRICAL CONTROL SYSTEM Filed Nov. 30, 1944' `L Il 4 1 5 Sheets-Sheet 2 INVENTOR.

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O. E. BOWLU'S ELECTRICAL CONTROL SYSTEM Filed Nov. 30, 1944 5 Sheets-Sheet 3 OCL 15, 1946. Q E BOWLUS I 2,409,534

ELECTRI CAL CONTROL SYSTEM Filed Nov. so, 1944 5 sheets-sheet 4 1 f z. :40 f te -g l' /Z f I l L f K 5v n L f\ w Jhr m 244m zal f4 ef [i3/4 www@ w1 Oct. l5, 1946. o. E. BowLus 2,409,534 v ELECTRICAL CONTROL ASYSTEM Filed Nov. 30, 1944 5 Sheets-Sheet 5 Patented Oct. 15, 1946 ELECTRICAL CONTROL SYSTEM Omer E. Bowlus, Detroit, Mich., assignor to Chrysler Corporation, Highland Park, Mich., a

corporation of Delaware Application November 30, 1944, Serial No. 565,954

zo onims. 1

The present invention relates to electrical control systems and is particularly directed to the provision of improved apparatus which functions as a combination converter-inverter for deriving alternating current energy of a desired adjustable frequency from a source of alternating current the frequency whereof may be randomly variable over a range which is above, below, or which includes, the output frequency. in its herein illustrated embodiments the present invention is particularly designed for aircraft purposes, and' closed but not claimed herein are claimed in thel copending application of the present applicant and Nims, Serial No. 565,S56, iiledNovember 3G, 1944, both f which applications are assigned to the assignee of this application.

Principal objects of the present-l invention are to provide a system of the aforesaid type which is simple in arrangement, requires a minimum number of structural elements, is relatively light in weight, and is reliable and eflicient in operation; to provide such a system in which multi-phase alternating current input energy is translated into multi-phase alternating current output energy; to provide such a system embodying improved means for timing the operations of the control apparatus associated with the several. output f phases; to provide such systems in which the multi-phase output circuits of the several units may be connected in parallel, and embodying improved means for synchronizing the control apparatus of the several units; and to generally improve and simplify the construction and arrangement of systems of the above generally indicircuit in parallel with each other. In reading the drawings, Figure 1B may be placed immediately to the right of Figure 1A, Figure 1C may be placed immediately below Figure 1A, and Figure 1D may be placed immediately below Figure 1B. When the drawings are so arranged uncon nected terminals on the various sheets will line up with correspondingly designated unconnected terminals on the adjacent sheets, thereby completing the circuits which extend from one sheet to another; and

Figure 2 is a 'series of curves depicting various operating characteristics of the system.

It will be appreciated from a complete understandingv of the present invention that in their broader aspects, the improvements thereof may be embodied in widely differing systems, arranged for widely differing specific purposes. The system specifically disclosed herein is particularly designed for use on multi-engine aircraft, to furnish three phase alternating current for various control and operating purposes. The disclosure herein of the invention with particular reference to this application is, however, to be regarded in an illustrative and not in a limiting sense.

As is indicated above, it is desirable, in connection with modern aircraft, to provide selfcontained generating systems of the alternating current type, which are adapted to deliver alternating current at an adjustably xed frequency and voltage, and which utilize, as a prime source of power, alternating current generators which are driven by the aircraft engines. Since the aircraft engine speeds vary rather widely in operation, the frequency of the alternating current generators also vary, making it desirable to provide apparatus which is effective to translate alterhating current of a variable frequency into current having a frequency which is adjustably fixed, and which may fall below, within, or above the frequency range of the generator. The aforesaid copending application of the present applicant Nims, Seria1 No. 565,955, filed November 30, 1944, discloses and claims certain features of such sys- 1 tems, which, as specifically disclosed, are effecnecting the output circuits of the two units in parallel. Similarly, Figures 1C and 1D show virtually identical control circuits for the power units of Figures 1A and 1B respectively and also show the synchronizing interconnections between such control systems. For these reasons a description of one powei` and one control unit will suffice for a description of both, except in the respects hereinafter noted.

Referring first to Figure 1A, power is arranged to be delivered to the three phase output conductors l0, 2, and I 4, from an alternating current generator I6, through a combination converterinverter comprising three series of main valves --22-24-26-28-30; 32-34--35--38-li0m 42; and 44--66-48--50-52-54.

Generator I6 may be of usual construction may be arranged to be driven either directly or, and preferably, through suitable change-speed gearing, by a corresponding engine of the aircraft. Generator IE is provided with a usual direct current field winding which, as described in the aforesaid Nims application, may be provided with regulating apparatus which serves to maintain the voltage of generator It' at a substantially uniform value through the expected generator operating speed range, which in the case of aircraft systems, may be from 4,000 to 10,000 R. P. M. Such regulating apparatus may also be arranged as described in the Nims application to maintain a proper division of the load between two or more of the present power units when such units are operated in parallel with each other.

Each of the aforesaid main valves may be of any conventional type. Preferably and as indicated they are usual three element gas-lled grid controlled Valves of the so-called discontinuous type. That is to say, each of these valves, though normally non-conductive, may be rendered conductive, when their anodes are surfV ciently positive with respect to their cathodes to sustain a discharge, by rendering their grids sufiiciently positive with respect to their cathodes. When so rendered conductive, the grids lose control and the valves remain conductive until the anodes are either negative with respect to their cathodes or are not sufficiently positive to sustain a discharge. It will be noticed that the cathodes of related groups of these valves are directly interconnected so that, although structurally separate valves are illustrated, multi-anode structures may be used instead. That is to say, for example, valves 20, 22, and 24 may be combined into a single multi-anode structure.

Generator I6 is illustrated as having 'six star connected phase windings A, B, C, D, E, and F, which are directly connected to the anodes of the corresponding main valves. That is to say, phase A is directly connected to the anodes of valve 2??, associated with output conductor I4, valve t2 associated with output conductor I2, and valve 48 associated with output conductor I0. Phase B in turn is connected to the anodes of valves 22, 38, and M associated respectively with output phases I4, I2, and I0. Corresponding comments apply to the other generator phases, it being noted that each generator phase is associated with and is effective to supply current, under the conditions hereinafter stated, to one phase of the output circuit.

The cathodes of the main valves associated with output phase I4 are connected to the respec tive terminals of the primary winding of an associated transformer 62. Similarly, the

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cathodes of the main valves associated with output phase I2 are connected to the terminals of the primary winding te of associated transformer 06, and the cathodes of the main valves associated with output phase I0 are connected to the terminals of the primary winding 53 of an associated transformer l0. Primary windings 0G, till, and 53 are provided with center taps which are connected through corresponding reactors l2, 14, and l5 to the center tap 'I3 of the generator it. Reactors '.'2, '14, and 'I6 may be and preferably are magnetically independent of each other, which relation is indicated by the dashed lines appearing therebetween.

Transformers 62, S0, and il are provided wi grounded secondary windings B, Bil, and B4, whi n as shown, are directly connected to the correspending load conductors I4, I2, and which load conductors for the two parallel units directly connected.

Commutating condensers S0, and con* nected directly across the corresponding transiformers 62, t6, and l0 and serve control the conductivity of the associated valves, in the hercinafter described manner.

To control the initiation and duration of vthe successive positive and negative half cycles of the output phases I4, |2, and i0, and to determine th displacement, in electrical degrees, between th voltages induced in such phases, correspondin control transformers I 00, |02, and |04 are pro-- vided. These control transformers are provided respectively with center tapped primary windings |06, |08, and H0, and are also provided respectively with pairs of secondary windings |I2 and ||4; ||6 and H3; and |20 and |22. The terminals of windings ||2 and H4 are connected, respectively in series with current limiting resistors |251, between the grids and cathodes of valves 20-22-24 and 25-20-30. Windings i5 and Ill, and |20 and |22 in turn areJ correspondingly connected between the grids and cathodes of the remaining associated valves.

In accordance with this embodiment of the present invention, alternating voltages of ajc proximately square wave form are induced in the secondary windings ||2| ill- I |6-| |8-i10- |22, the voltages in the two windings of each pair being 180 degrees out of phase with each other, and the voltages of the respective pairs being degrees out of phase with each other. The control circuits for eiecting such energization of the secondary windings of the control transformers are shown in Figures 1C and 1D, and are described hereinafter, As will be appreciated, and as is diagrammatically shown in portions 1V, V, and VI of Figure 2, the above-described control voltages render the grids of the associated main valves alternately positive and negative with respect to their cathodes, so as to cause successive positive and negative half cycles of voltage to be induced in the respective output windings 80* 82-84.

It is believed that the operation of the above described power circuits will be apparent from a description of the operation of the converterinverter circuits associated with, for example, the output phase I4. At the time ti in Figure control winding H2 becomes effective to positively bias the grids of Valves 20-22-24, and winding |l4 becomes effective to negatively bias the grids of the associated valves 25-2E2-30. ils is described below, the latter action prevents any discharges in the last-mentioned valves, and it will beA understood that the former action tends to render the valves 20--22-24 conductive. At the time t1, phase A is most strongly positive and, because of the common cathode connections of the last-mentioned valves, this fact renders the cathodes of valves 22 and `24 positive with respect to their anodes and prevents the initiation of a discharge therethrough. Valve 20 is, however, conductive, and current may flow therethrough from phase A through the left-hand half of the associated primary transformer winding B0, and through the corresponding reactor 12. At the time tz in Figure 2, the potential of phase B rises to a value surliciently in excess of the voltage of phase A to render valve 22 conductive, and initiate a flow of current from phase B through valve 22 and the left-hand half of primary winding E0. Conduction through valve 22 elevates the potential of the cathode of valve 29 to a value above that of its anode, and extinguishes the discharge through valve 20. Similarly, at approximately the time t3, the voltage of phase C rises to a Value above that of phase B, initiating a discharge through valve 24 and extinguishing the'discharge through valve 22.

The aforesaid flow of current from the source charges up the associated commutating condenser 86, bringing its left-hand terminal to a positive potential and its right-hand terminal to a negative potential. This full charge is preferably obtained just before each commutation point is reached, in this case, the time t4. Throughout this interval, phases D, E, and F are, to vary ing degrees, positive,` and the negative potential established for their cathodes by winding 60 and condenser 86, tends to cause ow of current through valves 26-28-30. Such current flow is prevented, however, by the strong negative bias applied to the grids of these valves by control winding I I4.

At the time t4 in Figure 2, the polarities of windings I I2 and I I4 are reversed, which reversed relation is maintained until the time te. The negative polarity of control winding I I2 negativa ly biases valves ZIJ-22-24 which action is without effect on valves 20 and 22 since these valves are not conducting at the time t4. The negative bias applied to the conducting valve 24 tends to extinguish the discharge therethrough, and may, with certain classes of valves, be effective to do so.

The positive bias applied to valves 26-28-30 by control winding II4 tends to render all of these valves conductive. At the time t4, however. phase F'is more positive than phases D and E and consequently valve 26 is the only one of the just-mentioned three valves which becomes conductive. This action initiates in the sense dis cussed below, the negative -half cycle of voltage of output phase I4. As soon as valve 26 becomes conductive, it elevates the right-hand terminal of condenser 86 to a value which is lower than the voltage of phase F by only the amount of the relatively small voltage drop through valve 26. By virtue of the charge then existing on condenser 86, this action immediately elevates the cathode potentials of all of valves 20, 22, and 24 to values well above their anode potentials and extinguishes any discharges existing therein. The reversal of the charging voltage applied to condenser 86 when valve 26 becomes conductive enables the initial charge to dissipate itself through winding 6G and further enables a. verse charge to be huilt up on condenser 85. This reverse polarity renders the cathodes of valves 20-22-24 strongly negative with respect to their anodes, which action is, however, ineffective to re-establish a discharge through any thereof in view of the negative bias applied to the grids. It is to be noted-that the time required for the discharge of condenser 86 is longer than the deionization time of the just-mentioned valves. Consequently, the grids of these valves are enabled to obtain control thereof and maintain them non-conductive as aforesaid. It is believed to be evident that at the time t5, the flow of current through winding 60 transfers from phase F and valve 25, to phase D and valve 28. Further, it is believed to be evident that at the time te, at which time the original polarities of windings II2 and VII4 are restored, valve 28 is extinguished, and the next succeeding positive half cycle of output phase I4 is initiated from phase B through valve 22. It will be noticed from portion I of Figure 2f that with the assumed frequency relations between the input and the output circuits, that during the rst above described positive half cycle of the output phase I4, phases A, B, and C successively deliver current, through valves 2ll-22-24. During the rst described negative half cycle on the other hand valves 2S and 28 carry the current, which is derived from phases F and D. During the positive half cycle represented by the interval ist?, valves 22 and 24 conduct current from phases B and C. It will thus be apparent that the number of phases and valves which supply current to output phase I4 varies during successive half cycles of the same polarity and during successive half cycles of different polarity. The full lines in portion I of Figure 2` indicate the time intervals throughout which the correspondingly designated phases are effective to supply current to output phase I4.

Considering now the general form of the voltage wave induced in the secondary winding of transformer 62, and the phase relation of this induced voltage relative to the output voltages of control transformer Ill, it will be appreciated that so long as valves 20-22-24 are conductive they tend to cause a ow of current through the lefthand half of the primary winding 60 of the associated output transformer, resulting in, for example, a positive half cycle of induced voltage in secondary winding 89. Conversely, when valves 26-23--30 are conductive they tend to cause a flow of current through the right-hand half of winding 6U and induce a half cycle of voltage of negative polarity in winding 89. The impedances in the converter-inverter network delay the induced voltage in winding 86 by a phase angle equal to a fraction of a half cycle of the output frequency. This delay or phase shift may, in a general sense, be explained as follows: At each commutation point, such as the time t4 in Figure 2, the commutating condenser 86 is charged, as aforesaid. When, at time t4, valve 26 becomes conductive, condenser 48 is enabled to elevate the potentials of the cathodes of valves 26-22-24 as aforesaid. Condenser 86 also elevates the potential of the center tap of winding 6D, These changes in potential are of course enabled by the associated reactor '1;2. The energy stored in condenser 86 prevents an immediate reversal of the induced voltage in winding Sil, such induced voltage falling to zero only after the expiration of an interval determined in part at least by the characteristics of the previously described dis-- charge circuit for condenser 86. Similar comments apply to the delayed reversal of the induced voltage in winding 8a which is initiated at each other commutation point such as the time te.

The form of the induced voltage wave in winding 80 is of course determined by the relative impedances in converter-inverter network as a whole and it is preferred to so proportion these impedances as to produce an induced voltage of approximately the wave form shown in the aforesaid Nims application.

It will be observed accordingly that although the transfer action between valve groups which takes place at each commutation point, does not necessarily result in an immediate reversal of the induced voltage in the corresponding output winding, such as 8G, such transfer action does initiate or result in such a reversal.

The operation of the valve banks associated with output phases I2 and I0 is the same as that described above with the exception that the control voltages applied to these banks are displaced 120 degrees with respect to each other and with respect to the control voltages for output phase I4. Portions II and III of Figure 2 indicate, in full lines, the intervals, with respect to the corresponding control voltages (portions V and VI respectively) during which the indicated phases are eifective to supply current to the corresponding output phases.

By examination of portions I, II, and III oi Figure 2, it will be noticed that at any given time, for example, the time t1, phase A is effective to deliver current for each of output phases I4 and I2 Beginning at the time tz, in turn phase D is effective to deliver current to each of output phases I2 and Il?. A particular generator phase, therefore, serves to deliver current to a plurality of output phases at the same time.

So long therefore as the above-mentioned synchronously timed control voltages are developed by the control transformers IM, |02, and |84, the six phase variable frequency input power is translated into a three phase output having a frequency equal to that of the energy applied to the control transformers. It will further be appreciated from the foregoing that the input and output :frequencies are virtually independent of each other, thus accommodating the system to the relatively unusual case in which the input and output frequencies are identical, as well as to the more usual case in which they differ. It should be noted that the loading of the individual phases of the generator has a substantially uniform average value, for any given output load, although at certain frequencies, the average loading of the individual valves is not uniform. More particularly, in the event the input and output frequencies are identical, certain of the main valves remain inactive if certain input and output phase relations exist. This circumstance `makes it desirable, of course, to utilise valves of sufficiently large capacity to reliably handle any unbalanced loading conditions.

It will be appreciated that in the broader aspects of the invention, the main generator may be provided with a different number of phases than the illustrated six phases. For example, a three phase generator may be used, as disclosed in the aforesaid Nims application. In utilizing a three phase generator it will be appreciated that each phase winding is connected to twice the number of anodes as in the present case. That is, a particular phase winding would be connected to all of the anodes to which, for example, phases A and D of the present generator are connected and so on.

Referring now to Figure 1C, the illustrated arrangement for energizing the above-described control transformers |00, |02, and |04 in the pre- Cil viously described accurately timed relation, comprises generally an oscillator circuit |33, which serves as a source of periodic voltage; a counternetwork |32, which serves to segregate successive impulses from the oscillator circuit and appropriate them in proper order to the respective output phases; and a series of three inverter networks I34 which respond to the counter-network and control the delivery of energy to the respective control transformers lili), W2, and |54.

The oscillator circuit I3@ may, in general, be of any usual type and as illustrated, comprises a usual grid controlled gas-filled valve I4@ of the previously mentioned discontinuous control type. Valve |40 is connected across terminals |42 and |44 of an illustrative source of power, in series with the primary winding oi a synchronizing transformer |46, a timing condenser |48, and a potentiometer resistor I 5E). Usual gas-filled voltage regulating glow tubes |52 and I5-I are interposed between terminals |42 and Illll and serve, as will be understood, to maintain the voltage between these just-mentioned terminals at a substantially uniform value, terminal M4 being grounded and terminal |42 being indicated, for illustrative purposes, as having a potential ci 24D volts. N eglecting the action of the synchronizin transformer ill, it will be appreciated that when valve Idil is conductive, current is enabled to flow therethrough and charge up condenser |48, which current flow is surge-like in character. By virtue of the inductance in the plate circuit of the valve, the completion of this charging action is accompanied by a momentary reversal of the voltage across the valve which temporarily renders its cathode positive with respect to its anode. This action blocks the valve and enables the energy stored in condenser |43 to dissipate itself through resistor |56. As this charge is progressively dissipated, the potential of the cathode of valve |40 is correspondingly lowered, thereby progressively increasing the anode-cathode voltage across the valve. When the latter voltage reaches a critical value valve MB again breaks down and passes an impulse of current. Valve |40 is thus rendered conductive and non-conductive periodically, at a frequency determined primarily by the characteristics of the discharge circuit for condenser |48, each conductive period being a very minor fraction of each non-conductive period. During each conductive period the potential of the adjustable tap 56 on resistor LED abruptly rises and during each non-conductive interval, such potential gradually falls to a normal value. The potential of tap |55 is thus of the usual saw-tooth wave form, as indicated in portion VII of Fig. 2.

The corresponding oscillator for the companion unit (Figure 1D) duplicates the unit just described, it being noted that the secondary winding of each synchronizing transformer is tied to the grid of the oscillator valve |43 for the other unit. More particularly, the grid cathode circuit for valve |49 of the unit shown in Figure lC extends from the ground terminal IM through the corresponding valve Idil, conductor |58, thence through the secondary winding IED of the companion synchronizing transformer |46 to the corresponding ground terminal IM (Figure 1D). It will be appreciated accordingly that each time valve |453 ci one unit breaks down, a voltage impulse is transmitted through the secondary winding of the corresponding winding synchronizing transformer |45, which voltage impulse breaks down the valve |40 associated with the other 9 unit. The oscillator circuits for the two units are thus caused to operate in synchronism with each other.

It will be appreciated that the output frequency of each oscillator circuit is determined primarily by the desired output frequency of the power circuit and by the number of phases of the power circuit. In the present arrangement three output phases are provided and two impulses per output phase are required from the oscillator circuit. Accordingly, assuming a 400 cycle output frequency, it will be appreciated that the oscillator circuits are adjusted to have a frequency of 2,400 cycles per second.

Each counter-network comprises primarily a series of three Valves, |62, |64, and |66, which preferably, but not necessarily, are of the high vacuum continuous control type. The cathodes of these valves are connected together and to the ground terminal |44. The anodes of these valves are connected, through control resistors |68, |10, and |12, to a supply conductor |14, which is maintained, by regulator valves |52 and |54, at an intermediate potential, of the order, for example, of 150 volts. The grids of valves |62 and |64 are continuously tied to terminal |16, which is intermediate resistor |12 and the anode of valve |66, which grid circuits include resistors |18, |80, and |82. The grid circuit for valve |62 also includes a delaying condenser |84, which functions as hereinafter described. Similarly, the grid circuits oi valves |62 and |66 are tied to terminal |86, which is intermediate resistor and the anode of valve |64. These grid circuits include resistors |88, |90, and |92 and the just-mentioned grid circuit for valve |'66 includes a delaying condenser |94. Finally, the grid circuits for valves |64 and 86 are tied to terminal |96, which is intermediate resistor |68 and the anode of valve |62. These grid circuits include as indicated a-delaying condenser |98 and resistors 200, 202, and 204. The grids of all of the counter-tubes are tied, in parallel with each other, to the previously described oscillator terminal |56. Each such grid circuit includes a small blocking condenser 206. It will be appreciated accordingly that each time a positive impulse is applied to terminal |56, such impulse is transmitted to the grids of the three counter-valves and correspondingly elevates the potentials of these grids to a positive value with of Figure 2, the potential of terminal |56 being shown in portion VII of such figure.

The functioning of this counter-circuit, in general, is such that, at any given time, two of the three counter-valves are conductive and the remaining counter-valve is non-conductive. Each time a positive impulse is delivered from the oscillator circuit to the grids of these valves, the nonconductive valve is fired or rendered conductive. This action does not alter the conductivity of one of the remaining two valves but it does extinguish the remaining valve. Thus, for example, during an interval between two successive impulses of the oscillator circuit, valves |62 and |64 may be conductive and valve |66 may be non-conductive. The next impulse fires valve |66 and extinguishes valve |62, leaving` valve |64 conductive. The next impulse from the oscillator circuit fires valve |62 and extinguishes valve |64, leaving valves |62 and |66 conductive. The next impulse from the oscillator circuit fires valve |64 and extinguish valve |66. More particularly, operation of the counter-network is as follows: Assuming that valves |62 and |64 are conductive, it will be appreciated that terminals |96 and |86 have potentials which are above ground by only the amount of the voltage drops through valves |62 and |64, the balance of the voltage between ground and conductor |14 being consumed in resistors |68 and |10. The grids of valves |62, |64, and |66 are connected through resistors 208, 2|0, and 2|2, to terminal 2|4, the potential whereof 1's somewhat below ground, for example, 35 to 50 volts below ground. The ratio of the resistors 204 and |90 (which are connected to the aforesaid terminals |96 and |86) to resistor 2|2 is such that under the conditions stated, the grid of valve |66 is negatively biased, which action renders valve |66 non-conductive. At the same time, the grids of valves |62 and |64 are connected through resistor on the one hand and resistor |82 on the other hand, to terminal |16. Since valve |66 is non-conductive, terminal |16 is at substantially the potential of conductor |14, which potential is very materially higher than that of terminals |96 and |86, and the last-mentioned connections thus serve to maintain the grids of valves |62-|64 at potentials which are slightly above ground and at which these valves are in wide-open condition.

t will be noticed that under the above described conditions the blocking condensers |84 and |98 receive charges, of the indicated polarities, the charge on condenser |84 attaining a value equal to the drop across resistor |80 and the charge on condenser |98 attaining a value equal to the drop across resistor 202.

Assuming now that the potential of terminal |56 associated with the oscillator circuit is abruptly elevated, as described above, by the flow of a surge current through the oscillator valve |40, it will be appreciated that this action applies a peaked positive impulse, also as aforesaid, to the grids of each of the counter-valves |62, |64, and |66, This action of itself, is without effect on valves |62 and |64, in view of the fact that the grids thereof are already at wide-open positive values. This action does, however, positively bias the grid of valve |66 and renders this valve fully conductive. As soon as valve |66 becomes fully conductive, it immediately lowers the potential of terminal |16 to a value which is above ground only by the amount of the relatively small voltage drop through valve |66, which potential is substantially the same as the previously described potentials of terminals |96 and |86. The drop in potential of terminal |16 tends to but does not negatively bias the grid oi valve |64, since this tendency is opposed by the impulse from oscillator circuit. The drop in potential of terminal |16, however, does immediately drive the grid of tube |62 to a negative potential, relative to its cathode, because of the charge on condenser |84. As soon as this action occurs, valve |62 becomes non-conductive and elevates the potential of terminal |96 to a value corresponding to the previously described potential of terminal |16; that is to a potential substantially equal to that of conductor |14. With terminal |96 at the relatively high potential, the grids of Valves |64 and |66 are held positive so that these valves are substantially wide-open, through circuits corresponding to those previously described in connection with valves |62 and |64. Similarly, with both valves |64 and 66 conductive, the grid of valve |62 is negatively biased in a manner analogous to that previously described in connection with the negative bias on the grid of valve li. The single described impulse from the oscillator circuit, therefore, serves to extinguish Valve |52, leaving valves and it conductive. It is believed to be evident that in an analogous manner, the next impulse from the oscillator circuit is effective, by ring valve |52, to extinguish valve |64, leaving valves |52 and |555 conductive. Similarly, a succeeding impulse is eiective, by ring valve 54 to extinguish valve |56, leaving valves |52 and |554 conductive.

Each on or conductive interval of each countervalve is therefore equal in length to twice the period of the oscillator circuit, and each oil or non-conductive interval of each counter-valve is equal to one period oi" the oscillator circuit. State-.fl in another way, each cycle comprising one on and one oil interval of each counter-valve, is equal in length to three periods of the oscillator. Moreover, the cycles of the respective counte valves have a phase displacement of one period of the oscillator; that is, a phase displacement of one third of a full cycle of cach counter-valve. These phase relations are indicated in portions IX, and XI, of Figure 2. Thus, assuming an oscilla-for frequency of 2,400 cycles, each counter-valve has a frequency of 8D!) cycles.

In the present system, each change from a nonconductive to a conductive condition of each counter-valve is utilized to trigger the correspond* ing inverter network iM. Each such inverter comprises a pair of high vacuum valves, designated 22), 222, 224, 22S, 228, and 23%. Each such valve comprises main and auxiliary anodes, a com trol grid and an indirectly heated cathode. Usual screen grid valves are usuable and are indicated in the drawings, the screen grids serving as the auxiliary anodcs. Since these inverter networks are identical, a description ol one thereof will suilice for all. Considering the inverter network associated with output phase I4, and which cornprises valves 229 and 222, the cathodes of these valves are connected to the ground conductor 'I'he anodes o these valves are connected to the corresponding terminals of the primary winding |06 of the associated control transformer llll, which winding has a center tap 23S which is continuously connected to supply conductor 2. 8, which is continuously maintained at al potential of, for example, 300 volts above ground. A stabilizing resistor 21.0 is connected across the pri mary winding |06. The screen grids 2M and of valves 220 and 222 are continuously connected., through control resistors 2li@ and 248, toa supply conductor 250 which is continuously maintained. at a. potential somewhat below the potential of. conductor 238. For example, conductor 25o may be maintained at a potential of approximately 240 volts above ground.

The control grid 252 of valve 22B is connected, through a network comprising a condenser 254 and a resistor 256, to terminal 253 which is intermediate resistor 248 and the anode of the companion valve 2'2. The control grid of valve 22 is similarly connected, through. a network comprising resistor 262 and condenser 254, to terminal 2&5. Grids 252 and 26|) in turn are interconnected together through condensers 268 and 21o. Conduc n tor 212, which is connected to the anode of the corresponding counter-valve |52, is connected to terminal 214, intermediate the last-mentioned condensers Conductor 212 includes a bloclringf condenser 215, and is connected to the ground conductor 232 through a relatively high resistance 218 and a continuously conductive rectifier 233,

of usual form. Grids 252 and 2E@ are also connected, through associated resistors 232 25M to conductor 28S which is continuously maintained at a potential well below ground; for eziample, at a potential of minus 240 volts.

At any given time one of the inverter valves 220-222 is conductive and the companion inverter valve is biased to a non-conductive condition. A feature of the present invention resides in. utilizing the anode-cathode circuit of each inverter valve to supply the associated control transformer IDD, through the abovemen tioned connections; and in utilizing the screen grids of these inverter valves as auxiliary anodeo to provide an output circuit for each valve to produce the inverter action. The inverter action may thus be described independently of the primary output circuits of these valves.

More particularly, and assuming that valve 22d is fully conductive, it will be appreciated that a substantial part, for example, two-thirds, oi" the voltage difference between. conductor 25B and the grounded cathode is consumed in resistor 24B, leaving terminal 255 at a potential which is above ground only by the amount oi the vol*- age drop through valve 222.

The impedance of the network between terminal 266 and the negative conductor 235, and comprising resistor 262, condenser 26d, and resistor 224 is such that terminal 238 of this network, to which grid 259 is connected, is at a sufficiently negative potential with respect to ground to completely bias valve 280 to a nonconductive condition. Under these conditions, the only voltage drop through resistor 2518 is due to the current flowing in the network connection between conductors 252 and 225, and comprising resistor 243, condenser 25d, resistor 255, and resistor 282. The impedance of this network is such that under the indicated conditions terminal 29ll, to which grid 252 is con'- nected, is maintained at a potential with respect to the cathode of valve 22S, at which this valve is in a wide-open condition. Under the above conditions, further, condensers 238 and 210 contain variable charges, depending upon the stage of the inverter cycle then in progress.

Each time counter-valve 152 changes from a conductive to a non-conductive condition, the potential of the associated terminal 292 abruptly rises, as will be clear from the previous description. This increase in voltage, except in negligible part, is not communicated to terminal 214 of the inverter circuit, since under the indicated conditions, rectifier 28|] ailords virtually a short-circuit between conductor 2i2 and ground. Such increase in voltage does apply a potential to and charge up the small blocking condenser 216.

Each time counter-valve |52 becomes conductive, the potential of terminal 292 abruptly falls to a considerably lower value, as will be clear from the previous description. This action immediately pulls terminal 293 down to a potential which is below the potential of terminal 292 by Athe amount of the charge on condenser 215.

The constants of the circuit, including terminals` 290 and 292, are such that the just-mentioned drop in the potential of terminal 290, produced by valve |2, is transitory in character.

The peaked negative impulse (portion XII, Figure 2) thus applied to terminal 25B serves to reduce the positive bias of he grid of valve 226. This action in turn decreases current flow between its cathode and its auxiliary anode or 13 screen grid 242. The latter action in turn de` creases the voltage drop across resistor 246, thereby elevating the potentials of terminals 266 and 288 and opening up valve 222. rIChe opening of valve 222 increases the drop across resistor 248 and correspondingly lowers the potentials of terminals 258 and 202. The lowering of the potential of terminal 290 still further reduces the conductivity of valve 220 which is reflected as an increase in the conductivity of valve 222. The above described negative impulse accordingly serves to initiate a progressive swing of valves 220 and 222, which swing takes place exceedingly rapidly, with respect to the frequencies involved in the present system, and serves to completely open valve 222 and completely block orl valve 220.

The next time counter-valve I 62 becomes nonconductive, the positive impulse applied to terminal 292 is suppressed as before, making no change in the. conductivities of the inverter valves. On the other hand, the next time counter-valve |62 becomes non-conductive, a peaked negative impulse is again applied to terminal 214. Since the inverter circuit is symmetrical, it will be appreciated that this negative impulse serves to block off valve 222 and render valve 220 fully conductive. Under the as-l sumed conditions of a frequency of 800 cycles for the action of counter-valve 162, it wiil be appreciated that each of the inverter valves is thus cycled by the conductive and non-conductive conditions at the rate of 800 times a second, which corresponds to a frequency of the inverter circuit of 400 cycles.

Considering now the principal output circuits of the inverter valves, it will be appreciated that so long as inverter valve 220 is conductive, current iiow in the corresponding portion of thc primary winding of the associated control transformer is in a direction to establish `one polarity for the secondary or output windings H2 and H4 of this transformer. So long as valve 222 is conductive, on `the other hand, an opposite polarity is established for windings |I2 and H4.

As previously mention, it is preferred that the output voltages of windings H2 and I|4 be of square wave form. Accordingly, in the present system, the impedance of the main anode-cathode circuits ofinverter Valves 220 and 2.22, are such that when either of these valves is rendered conductive, current through the corresponding main anode circuit rises gradually and Substantially linearly to a maximum value, which is attained at approximately the same time that the next inverter or flip-dop action occurs. When such action occurs current flow in the just-mentioned circuit is abruptly interrupted and a gradual rise in current flow through the main anode circuit of the other inverter valve is initiated. Current flow in the primary winding portions of the control transformer |00 is consequently of saw-tooth form and results in the approximately square wave form secondary outputs indicated in portion IV of Figure 2.

It is believed to be evident that the inverter networks comprising valves 224-226 and valves 228-230 function in the manner described above in connection with valves 220-222, in response respectively to the change from non-conductive to conductive condition of the associated countervalves |64 and |66. Consequently, transformers |00-I 02-| 04 deliver square wave secondary outputs having phase displacements of 120 electrical 14` degrees, the frequency of such outputs being determined by the adjustably fixed frequency of the associated oscillator circuit |30.

A further feature of the present invention resides in providing means to properly synchronize the counter-networks for the several units.

Referring to Figures 1C and 1D together, it will be noticed that auxiliary valve 300 is provided. This valve may be of usual three element high vacuum type. The anode of valve 3&0 is continuously connected to the grid 302 of valve |66 in Figure 1D. The cathode of valve 300 is continuously connected to terminal 2 I4 which as indicated is somewhat below ground, and the grid thereof is continuously connected to terminal 304, which is negative with respect to terminal 2 I4. It will be appreciated from a previous description that while Valve IEB of Figure 1C is conductive, the potential of terminal 308 is relatively low. Assuming control switch 306 is closed, with valve |166 conductive, it will be appreciated that the difference in potential between terminals 308 and SIG is absorbed in condenser 3|2, leaving the grid of valve 300 negatively biased. The connection between valve 300 and valve |66 of Figure 1D is thus without effect. As soon, however, as Valve #56 of Figure 1C is extinguished, the potential of terminal 306 is abruptly elevated, thereby positively biasing valve 300 and rendering it conductive. valve 300 is rendered conductive, it brings the potential of the grid 302 of valve |66 (Figure 1D) to a strongly negative value with respect to its cathode. such valve E66 is non-conductive (which is the condition assuming the counter-circuits for the two units are in proper step with each other) Such negative biasing is without eiiect. If, however, the counter-circuits should be out of step with each other, such negative biasing would immediately extinguish valve |66 of Figure 1D. Such extinguishment would have the same effect as though it had been caused by an impulse by the associated oscillator circuit. The just-mentioned synchronizing circuit thus serves to insure, when the units are placed in operation, that they are in proper step with each other.

A further feature of the invention resides in the provision of improved means for insuring that the inverter networks for each unit are in proper step with each other, and to further insure that such inverter networks for a plurality of units are in step with each other. The need for such synchronization arises, as will be understood, from the fact that a negative impulse from, for example, counter-Valve |62, is effective to re one or the other of the two inverter valves 220 and 222, depending upon which of these valves was last fired. As shown, conductors 234 and 235` serve to connect the control grids of valves 220 and 224 respectively, to the auxiliary anode or screen grid 231 of valve 230, through small blocking condensers 239 and 24 I. It will be appreciated that in view of the phase relations established by the counter-network, three of the inverter' valves 1220, and so forth, are conducting at any given time and moreover each time inverter valve 228 is rendered conductive, valves 220 and 224 should already be in a conductive condition. It will be appreciated that each time inverter valve 228 is rendered conductive, the potential of screen grid 231 of valve 230 rises sharply. This positive impulse is communicated, through the blocking condensers 239 and 24| to the control grids of Valves 220 and 224. If these valves are already conductive (which is the condition if the inverter If at the time this occurs,

15 circuits are in proper' step with each other), these positive impulses are without effect. Ii?, on the other hand, either of valves 220 and 224 should be non-conductive (which is the condition if the inverter networks are out of step) such positive impulse would immediately render the non-conductive valve conductive and bring the circuits into step with each other. It will be noticed that the above synchronizing circuits are provided for both units, Figures 1C and 1D.

In addition, in order to insure that the inverter .networks for both units are in proper step with each other, the screen grid of valve 230 for the unit of Figure 1C, is arranged for connection, through a small blocking condenser 243 and a normally opened manually operable synchronizing switch 245, to the control grid 24'! of inverter valve 228 associated with the unit of Figure 1D. With this arrangement, it will be noted that each time inverter valve 228 of Figure 1C becomes conductive, the consequent rise in potential of the associated screen grid 231 of valve 230, causes a positive impulse to be transmitted to the control grid of valve 228 associated with the unit of Figure 1D. If this valve is already conductive (which is the condition if the inverter networks for the two units are in step), this positive impulse is Without effect. On the other hand, if such networks are out of step, such impulse brings them into step.

In the present instance no source of energy for supplying the direct current power circuits has been indicated. It will be understood that these power circuits may be supplied from any suitable source. For example, a portion of the threephase output of the system may be utilized for this purpose. Alternatively, and as is described in more detail in the aforesaid copending Nims application, an auxiliary or pilot generator may be provided to supply the control energy.

Although only a single complete embodiment of the invention has been described in detail, it will be appreciated that various modifications in the form, number, and arrangement of the parts may be made without departing from the spirit and scope of the invention.

What is claimed is:

1. In a system for supplying a multiphase alternating current output circuit from a source of electric energy, the combination of a plurality of translating units individual to said phases, each unit including means actuable to translate energy from the source into single phase alterhating current energy and deliver the same to a corresponding phase of said output circuit, and i control means for actuating said units in predetermined phase relation to each other so that the respective phases of the output circuit have corresponding phase relations, said control means including a source of periodic control voltage common to said units, a network having a plurality of output circuits individual respectively to said units, means rendering said network responsive to said source of control voltage for energizing said output circuits in rotation, and means rendering each circuit operably responsive to each energization of the corresponding output circuit of said network.

2. In a system for supplying a multiphase alternating current output circuit from a source of electric energy, the combination of a plurality of translating units individual to said phases, each unit including means actuable to translate energy from the source into single phase alternating current energy and deliver the same to a correspond- LLO ing phase of said output circuit, and control means for actuating said units in predetermined phase relation to each other so that the respective phases of the output circuit have corresponding phase relations, said control means including a source of periodic control voltage common to said units, a network having a plurality of output circuits individual respectively to said units, means rendering said network responsive to said source of control voltage for energizing said output circuits in rotation, an inverter network individual to each unit and actuable in response to successive energizations to actuate the corresponding control means, and means rendering said inverter networks operably responsive to successive energizations of the corresponding output circuits of said inst-mentioned network.

3. In a system for delivering mtiltiphase alternating current energy to an output circuit from a source of multiphase alternating current energy, a plurality of translating units each individual to a corresponding phase of said output circuit, each unit comprising a pair of valve means each defining a plurality of discharge paths having a common cathode connection and a pltuality of anodes coupled to corresponding phases of said source, means coupling the valve means of each unit to the corresponding output phase so that current flow through the individual means of each pair tends to cause, respectively, current ilow of respectively opposite polarity in the corresponding phase of the output circuit, periodically actuable control means for each unit for successively rendering the corresponding valve means conductive and non-conductive in alternate relation, and timing means for actuating the several control means in predetermined phase relation to each other, said timing means including a source of periodic control voltage common to said units, a network having a plurality of output circuits individual respectively vto said units, means rendering said network responsive to said source of control voltage for energizing said output circuits in rotation, and means rendering each control means operably responsive to each energization of the corresponding output circuit of said network.

4. In a system for delivering multiphase alterhating current energy to an output circuit from a source of multiphase alternating current enorgy, a plurality of translating units each individual to a corresponding phase of said output circuit, each unit comprising a pair of valve means each dening a plurality of discharge paths having a common cathode connection and a plurality of anodes coupled to corresponding phases of said source, means coupling the valve means of each unit to the corresponding output phase so that current Flow through the individual means of each pair tends to cause, respectively, current now of respectively opposite polarity in the corresponding phase of the output circuit, periodically actuable control means for each unit for successively rendering the corresponding valve means conductive non-conductive in alternate relation, and timing means for actuating the several control means in predetermined phase relation to each other, said timing means including a source of periodic control voltage common to said units, a network having a plurality of output circuits individual respectively to said units, means rendering said network responsive to said source of control voltage for energizing said output circuits in rotation, an inverter network individual to each unit and actuable in response to 17 successive energizations to a'ctuate the corresponding control means, and means rendering said inverter networks operably responsive tosuccessive energizations of the corresponding output circuits of said Erst-mentioned network.

5. In a system for controlling iiow of current between a source and a multiphase lo-ad circuit, control moans individual to each phase of said load circuit, a source of periodic voltage common to said phases, a network having a plurality of output circuits individual to such phases, means rendering said network responsive to said source of control voltage for energizing said output circuits in rotation, and means rendering said control means operably responsive to energization of the corresponding output circuit.

6. In an inverter network, the combination of a pair of electric valves each having a cathode, a control grid and main and auxiliary anodes, means including control means coupling the auxiliary anode and grid circuits of said valves together to control the conductivity of said valves, and an output circuit coupled to the main-anodecathode circuit of each valve.

7. In an inverter network, the combination of a pair of electric valves each having a cathode, a control grid and main and auxiliary anodes, means including control means coupling the auxiliary anode and grid circuits of said valves together to control the conductivity of said valves, an output circuit coupled to the main-anodecathode circuit of each valve, and means for periodically actuating said control means to extinguish one valve and render the other valve conductive.

8. In an inverter network, the combination of a pair of electric valves each having a cathode, a control grid and main and auxiliary anodes, means including control means coupling the auxiliary anode and grid circuits of said valves together tov control the conductivity of said valves, translating means having a winding, the respective terminals whereof are connected tc the main anodes of said valves, said winding having an intermediate terminal, and a source of energy connected between said intermediate terminal and the cathode of said valves.

9. In an inverter network, the combination of a plurality of pairs of electric valves, each having a cathode, a grid and main and auxiliary anodes, means including control means coupling the auxiliary anode and grid circuits of the valves of each pair together to contro-l the conductivity of the corresponding valves, timing means to periodically actuate said control means to extinguish one valve of each pair and render conductive the other valve of such pair, an output circuit coupled across the cathode and main anode circuit of each valve of each pair, and means to energize said timing means of the respective pairs in predetermined phase relation to each other.

10. In an inverter network, the combination of a plurality of pairs of electric valves, each having a cathode, a grid and main and auxiliary anodes, means including control means coupling the auxiliary anode and grid circuits of the valves of each pair together to control the conductivity of the corresponding valves, timing means to periodically actuate said control means to extinguish one valve of each pair and render conductive the other valve of such pair, an output circuit coupled across the cathode and main anode circuit of each valve of each pair, and means to energize said timing means of the respective pairs in predetermined phase relation to each other, said lastmentioned means including a source of periodic voltage, a network having a plurality of output circuits effective respectively to so energize said timing means, and means rendering said output circuits successively responsive to said source of periodic voltage.

11. In a system for controlling ow of current to a multiphase load circuit, a plurality of networks each having an output circuit individual to each phase of the load circuit for controlling such phase, a valve for each output circuit, changes in conductivity of said valves serving to control the corresponding output circuits and effect said control, a pair of independently operable control means so constructed and arranged that each network is controlled by a different one 0i said control means for successively altering the conductivities of the valves of each network, and means responsive to one network for periodically correcting any out of phase of the other network so as to maintain the networks in step with each other.

12. Apparatus for supplying a multiphase load circuit comprising a plurality of systems each as deiined in claim l, means connecting the respective output circuits in parallel to said load circuit, and synchronizing means for causing the control means for the respective systems to be actuated in predetermined timed relation to each other.

13. Apparatus for supplying a multiphase load circuit comprising a plurality of systems each as deiined in claim 2, means connecting the respec tive output circuits in parallel to said load circuit, and synchronizing means for causing the control means for the respective systems to be actuated in predetermined timed relation to each other.

14. In a system for delivering multiphase alternating current energy to an output circuit from a source of mt. aphase alternating current energy, a plurality or translating units each individual to a corresponding phase of said Output circuit, each unit comprising a pair of electric valve means each defining a plurality of discharge paths having a common cathode connection and a plurality of anodes coupled to corresponding phases of said source, means coupling the valve means of each unit to the corresponding output phase so that current flow through the individual means of each pair tends to cause, respectively, current iiow of respectively opposite polarity in the corresponding phase of the output circuit, periodically actuable control means for each unit for successively rendering the corresponding valve means conductive and nonconductive in alternate relation, a source of periodic control voltage common to said units, a counternetwork including an electric valve'individual t0 each phase of the aforesaid output circuit, means coupling said valves to said source of periodic control voltage so that the conductivities of said valves are altered in predetermined succession, and means rendering each control means operably responsive to the condition of the associated said valve.

15. In a system for supplying a multiphase alternating current output circuit from a source of electric energy, the combination of a plurality of translating units individual to said phases and common to said source, each unit including means actuable to translate energy from the source to single-phase alternating current energy and delivering the same to a corresponding phase of said output circuit, a source oi periodic control voltage common to said units, a counter-network including an electric 4valve individual to each phase of the aforesaid output circuit, means coupling said valves to said source oi' periodic control voltage so that the conductivities of said valves are altered in predetermined succession, and means including an inverter network individual to each phase of the output circuit, each such inverter network being operably responsive to the condition of the associated electric valve.

16. In a system for delivering multiphase alternating current energy to an output circuit from a source of multiphase alternating current energy, a plurality of translating units each individual to a corresponding phase of said output circuit, each unit comprising a pair of electric valve means each deiining a plurality of discharge paths having a common cathode connection and plurality of anodes coupled to corresponding phases of said source, means coupling the valve means of each unit to the corresponding output phase so that current flow through the individual means of each pair tends to cause, respectively, current flow of respectively opposite polarity in. the corresponding phase of the output circuit, pc iodically actuable control means for each unit for successively rendering the correspending valve means conductive and nonconductive in alternate relation, a source of periodic control voltage common to said units, a counternetwork including an electric valve individual to each phase of the aforesaid output circuit, means coupling said valves to said source or" periodic control voltage so that the conductivities of said valves are altered in predetermined succession, and means including an inverter network individual to each phase of the output circuit, each such inverter network being operably responsive to the condition of the associated electric valve.

17. In a system for producing multiphase control voltages, the combination of a source of periodic control voltage common to such phases, a counter-network including an electric valve in dividual to each such phase, means coupling said valves to said source of periodic voltage so as to alter the conductive conditions of said valves in rotation, and means operably responsive to the lil 20 condition of each valve for producing a control voltage for the corresponding phase.

18. In a system for producing multiphase control voltages, the combination of a source of periodic control voltage common to such phases, a counter-network including an electric valve individual to each such phase, means coupling said valves to said source of periodic voltage so as to alter the conductive conditions of said valves in rotation, and means including an inverter network individual to each said valve and operably responsive to the condition thereof for producing a control voltage for the corresponding phase.

19. In `a system for controlling flow of current to a multiphase load circuit, a plurality of networks each having an output circuit individual to each phase of the load circuit for controlling such phase, said networks comprising a pair of independently operable control means so constructed and arranged that each network is controlled by a different one of said control means to actuate the corresponding output circuits in rotation, and means responsive to one network for controlling the other network so as to correct any out-of-phase operation of the other network with respect to the one network whereby the networks will be brought periodically in step with each other.

20. ln a system for controlling flow of current to a multiphase load circuit, a plurality of networks each having an output circuit individual to each phase of the load circuit for controlling such phase, said networks comprising a pair oi independently operable control means so constructed and arranged that each network is controlled by a different one of said control means to actuate the corresponding output circuits in rotation, means responsive to one network for controlling the other network so as to correct any out-of-phase operation of the other network with respect `to the one network whereby the networks will be brought periodically in step with each other, and means for selectively rendering said responsive means effective or ineffective.

OMER E. BOVVLUS. 

